US5278400A - Multiple threshold encoding of machine readable code - Google Patents
Multiple threshold encoding of machine readable code Download PDFInfo
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- US5278400A US5278400A US07/742,965 US74296591A US5278400A US 5278400 A US5278400 A US 5278400A US 74296591 A US74296591 A US 74296591A US 5278400 A US5278400 A US 5278400A
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- 239000000758 substrate Substances 0.000 claims abstract description 15
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- 238000012545 processing Methods 0.000 description 11
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- 238000013500 data storage Methods 0.000 description 1
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- 238000001514 detection method Methods 0.000 description 1
- 230000006870 function Effects 0.000 description 1
- 238000005286 illumination Methods 0.000 description 1
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Images
Classifications
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
- G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
- G06K7/14—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation using light without selection of wavelength, e.g. sensing reflected white light
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
- G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
- G06K19/06009—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code with optically detectable marking
- G06K19/06037—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code with optically detectable marking multi-dimensional coding
Definitions
- This invention relates to a method and apparatus for the recording and reading of encoded digital data on hardcopy recording media and, more particularly, to the use of codes composed of a plurality of cells each having a plurality of pixels.
- Plain paper is a favored recording medium for storing and transferring human readable information
- the emergence of electronic document processing systems has enhanced the functional utility of plain paper and other types of hardcopy documents by enabling the application of machine readable digital data thereon.
- This machine readable data enables the hardcopy document to actively interact with such a document processing system in a variety of different ways when the document is scanned into the system by an ordinary input scanner. See, for example, the copending and commonly assigned U.S. patent applications of Frank Zdybel, Jr. et al. and Walter A. L.
- digital data is recorded by writing two dimensional marks on a recording medium in accordance with a pattern which encodes the data either by the presence or absence of marks at a sequence of spatial locations or by the presence or absence of mark related transitions at such locations.
- Ordinary magnetic and optical digital data recording conform to this style of encoding.
- the digitized CCD output of the scanner is binary thresholded, and then the interpreting algorithm determines whether the 16 pixel cell has an 8 pixel black slash in it. If there is no slash, the pattern is interpreted as encoding a 0.
- the above system also suggests an encoding scheme wherein slashes of different directions are used to differentiate between a 0 and a 1. In such arrangements, the analog output is digitized and then binary thresholded.
- each cell of the image is a 4 ⁇ 4 matrix of pixels.
- the encoding of each cell consists in defining a diagonal marking in the cell, in the form of black image of 8 pixels, in a rotationally dependent manner. Accordingly, a cell having such a properly oriented marking corresponds to a 1, whereas a cell with no darkened pixels corresponds to a 0. With this encoding, it is apparent that the illustrated 8 cells (128 pixels) of FIG. 6 corresponds to binary 01111001, or decimal 121.
- the present invention is directed to the provision of a method and apparatus for encoding and decoding of data on a hardcopy, that enables the efficient and reliable recovery of the data while employing a minimum area of the hard copy.
- a method and apparatus are provided for encoding data on a substrate and decoding the coded data, wherein the data is in the form of a plurality of cells on the substrate, and each cell has a predetermined number of pixel locations.
- the encoding is effected by marking a number of the pixels, preferably by binary marking, the number corresponding to the data to be encoded. The relative location of the marked pixels in a cell does not constitute a part of the encoding.
- the gray scale level at each pixel of the cell is detected and converted to a corresponding digital signal.
- the digital signals corresponding to all of the pixels in the cell are summed.
- a plurality of different threshold levels are established dividing the maximum range of possible sums into subranges, and the sum of the digital signals is compared with the threshold values to determine the subrange within which the sum falls.
- the threshold levels are set so that the subranges correspond to the expected sums when corresponding numbers of pixels are marked. Accordingly, a signal corresponding to a determined subrange is output, to correspond to the encoding of the cells.
- FIG. l is a simplified block diagram of an electronic document processing system for carrying out and taking advantage of the various aspects of the present invention
- FIG. 2 is functional block diagram of a typical processor/printer interface for the document processing system shown in FIG. 1;
- FIG. 3 is an illustration of an image cell in accordance with one embodiment of the invention.
- FIG. 4 is an illustration of a group of image cells in accordance with the embodiment of the invention of FIG. 3;
- FIG. 5 is a simplified flow diagram of the method of the invention.
- FIG. 6 is an illustration of a group of image cells in accordance with patent application Ser. No. 07/560,514 as prior art.
- FIG. 1 illustrates an electronic document processing system 21 which may constitute a typical environment for this invention.
- the document processing system 21 comprises a digital processor 22 having a main memory 23 and a mass memory 24, an input scanner 25 for scanning digital representations of selected hardcopy documents into the processor 22, and a printer 26 for printing hardcopy renderings of selected ones of the files that are listed on a file directory (not shown) of the processor 22.
- a user interface 27 is provided for enabling a user to interact with the processor 22, the input scanner 25, and the printer 26.
- the processor 22 sets operations including setting thresholds, summing digital signals, and comparing the sum to the thresholds.
- the user interface 27 collectively represents the input devices through which the user enters control instructions for the input scanner 25 and for the printer 26, as well as the image editing and manipulation instructions for the processor 22. Additionally, the interface 27 represents the output devices through which the user receives feedback with respect to the actions that are taken in response to the instructions that are entered by the user or otherwise, such as under program control.
- the user interface 27 generally includes a keyboard or the like for entering user instructions, a monitor for giving the user a view of the process that is being performed by the processor 22, and a cursor controller for enabling the user to move a cursor for making selections from and/or for entering data into a process that is being displayed by the monitor. Since these components are conventional they are not illustrated herein.
- the illustrated document processing system 21 is centralized, so it has been simplified by assuming that all control instructions and all image editing and manipulation instructions are executed by the processor 22 under program control. In practice, however, the execution of these instructions may be handled by several different processors, some or all of which may have their own main memory and even their own mass memory. Likewise, either or both of the input scanner 25 and the printer 26 may have its own user interface, as indicated by the dashed lines 28 and 29, respectively. Indeed, it will be evident that the document processing system 21 could be reconfigured to have a distributed architecture to operate with a remote input scanner and or a remote printer (not shown). Data could be transferred from and to such remote scanner and printer terminals via dedicated communication links or switched communication networks (also not shown).
- the input scanner 25 may include a CCD 25A for scanning a hardcopy input document.
- the CCD is controlled by the processor 22 to selectively apply its outputs, corresponding to the different printed pixels, to an A/D converter 25B.
- the digital outputs from the A/D are stored in a memory of the system.
- the scanner is controlled by the program of the processor to scan the image of each hardcopy input document at a predetermined spatial resolution of, say, 300 s.p.i. ⁇ 300 s.p.i. (spots/inch).
- the CCD 25A converts the gray level of the individually resolved picture elements (commonly called “pixels” or “pels”) of the scanned image into corresponding analog values and the A/D converts these values to digital values for application to the processor and suitable storage.
- pixels commonly called "pixels” or "pels”
- the A/D converts these values to digital values for application to the processor and suitable storage.
- the printed pixel spatial resolution is equal to the CCD pel resolution (e.g. 300 spi by 300 spi) and that the program controls the maintenance of the alignment of the printed pixels with the array of the CCD pels.
- the printer 26, generally is a so-called bitmap printer for mapping the digital values of a bitmapped image file into the spatially corresponding pixels of the image it prints on a suitable recording medium, such as plain paper.
- the processor 22 may be configured to manipulate and store bitmapped image files and to transfer such files on demand to the printer 26.
- the processor 22 may include a PDL (page description language) driver 31 for transferring to the printer 26 PDL descriptions of the electronic document files that are selected for printing.
- the printer 26 is illustrated as having a PDL decomposer 32 for decomposing such PDL descriptions to produce corresponding bit-mapped image file. Still other types of printers and processor printer interfaces will suggest themselves, but it will be assumed for purposes of the following discussion that the printer 26 is a bitmap printer that receives PDL files from the processor 22.
- the image to be printed on hardcopy is separated into cells, each of which contains a predetermined number of pixels.
- a cell 30 may include 6 pixels arranged in a 2 ⁇ 3 array, as illustrated in FIG. 3.
- the cell is encoded by distinctively marking the pixels.
- a predetermined number of the pixels from 0 to 6, may be printed to be black, while the remaining pixels, if any are white. Accordingly, there are seven possible black-white combinations of the pixels of the cell.
- the specific location of the black pixels in each cell is not material, i.e. the encoding of the invention is concerned only with the number of distinctly marked pixels, and not their relative locations.
- the cell of FIG. 3 is thus illustrated to show a cell in which 4 of the 6 pixels are marked. It will be understood, of course, that the invention is not limited to the provision of cells of 6 pixels, and that either a greater number or a lesser number may be employed.
- characteristics of the marking of the marked pixels are preferably the same, i.e. there is no intentional variation in the detection characteristics of the marked pixels.
- the coded image cells are preferably binary printed on the substrate or hardcopy, rather than being printed at different gray scale levels. This technique results in more robust printing, and the printed code is less sensitive to illumination and process non-uniformities.
- the invention since a multiple pixel cell is printed with binary printing, rather than printing a single pixel cell with gray scale coding, the error rate on scanning of the cell is substantially reduced.
- the invention takes advantage of the gray levels available in a scanning CCD output signal, e.g. 128 gray levels.
- FIG. 4 illustrates the combination of 3 cells 30, each having 6 pixels in accordance with the arrangement of FIG. 3. Since each of the cells may correspond to any of 7 distinct non-spatially sensitive outputs, it is evident that the combination of 3 cells of FIG. 4, corresponds to any of 7 3 different outputs, e.g. any value from 0 to 343. as a consequence, the present encoding system enables the encoding of more than the 256 ASCII character set with only 18 pixels. As will be discussed, the pixel representation of FIG. 4 may correspond to the number "121". This contrasts, for example, with the rotationally variant binary thresholding encoding scheme of application Ser. No. 560,514, as illustrated in FIG. 6, wherein it was necessary to employ 128 pixels to represent the same decimal number.
- the output of the CCD 25A corresponds to the gray scale level of the sensed pixel, as indicated in FIG. 5 at block 51.
- This output is directed to an A/D converter 25B, as indicated at block 52 of FIG. 5.
- the 8 bit output of the converter can represent any integer from 0 to 255. If one of the bits is discarded due to noise, the remaining 7 bits of the A/D output can represent any integer from 0 to 127.
- the analog signal output of the CCD, corresponding to each scanned pixel may be converted into a digital number representing any decimal value from 0 to 127.
- the pixels 31 of a cell 30 are arranged in a 2 ⁇ 3 array.
- there are 7 possible distinguishable output levels from the CCD scanning each cell (assuming that the pixels of the cell are binary marked), depending upon the number of pixels that are black (or have other distinctive marking), i.e. from 0 to 6 pixels may be black.
- the digital values corresponding to all of the pixels of the cell are summed, to provide a sum S, as indicated at block 53, and the sum S of the sensed levels is tested at multiple threshold values, as indicated at block 54.
- the digital signal corresponding to each pixel may have a maximum of 2 L different values, and the sum S of the detected levels may have a maximum value of N ⁇ (2 L -1).
- N different threshold levels are defined, separating said maximum value N ⁇ (2 L -1) into N+1 level ranges.
- the threshold levels are selected in order to provide the maximum possibility that the range of values within which the sum S falls corresponds to the actual number of pixels that are distinctively marked (i.e. are black).
- the following threshold ranges may be employed:
- a comparison is made between the threshold values and the sum S to determine the range into which the sum S falls, and at block 55 a signal corresponding to this determined range is output, and constitutes the decoded value of the cell.
Abstract
Description
TABLE 1 ______________________________________ Threshold Level S Value Corresponding (Equal to or (within the Output (Number of less than) range) Black Pixels) ______________________________________ 63 0-63 6 190 64-190 5 317 191-317 4 444 318-444 3 571 445-571 2 668 572-668 1 762 669-762 0 ______________________________________
Claims (8)
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
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US07/742,965 US5278400A (en) | 1991-08-19 | 1991-08-19 | Multiple threshold encoding of machine readable code |
JP20514592A JP3262183B2 (en) | 1991-08-09 | 1992-07-31 | Method and apparatus for decoding a cell of an image having a plurality of pixels |
Applications Claiming Priority (1)
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US07/742,965 US5278400A (en) | 1991-08-19 | 1991-08-19 | Multiple threshold encoding of machine readable code |
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US5278400A true US5278400A (en) | 1994-01-11 |
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US07/742,965 Expired - Lifetime US5278400A (en) | 1991-08-09 | 1991-08-19 | Multiple threshold encoding of machine readable code |
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Cited By (52)
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US5459307A (en) * | 1993-11-30 | 1995-10-17 | Xerox Corporation | System for storage and retrieval of digitally encoded information on a medium |
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US5619026A (en) * | 1995-01-04 | 1997-04-08 | International Business Machines Corporation | Grayscale barcode reading apparatus system including translating device for translating a pattern image into a sequence of bar widths and transition directions |
EP0825547A2 (en) * | 1996-08-23 | 1998-02-25 | Matsushita Electric Industrial Co., Ltd. | Two-dimensional code reader |
US5761686A (en) * | 1996-06-27 | 1998-06-02 | Xerox Corporation | Embedding encoded information in an iconic version of a text image |
US5765176A (en) * | 1996-09-06 | 1998-06-09 | Xerox Corporation | Performing document image management tasks using an iconic image having embedded encoded information |
US5864127A (en) * | 1996-10-10 | 1999-01-26 | Xerox Corporation | Analog glyph detector and detector arrays |
US5898166A (en) * | 1995-05-23 | 1999-04-27 | Olympus Optical Co., Ltd. | Information reproduction system which utilizes physical information on an optically-readable code and which optically reads the code to reproduce multimedia information |
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EP0921492A1 (en) * | 1997-12-05 | 1999-06-09 | Datalogic S.P.A. | Method of compensating the edge positions of a signal generated by scanning a bar code |
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US5946414A (en) * | 1998-08-28 | 1999-08-31 | Xerox Corporation | Encoding data in color images using patterned color modulated image regions |
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